Ceramics are an ideal candidate for replacing metal-based restorative materials. Ceramics provide excellent chemical durability, wear resistance, biocompatibility, environmental friendliness, and esthetics. Nevertheless, widespread all-ceramic restoration use has been hindered by concerns related to marginal fracture resistance and clinical longevity. The overall goal of this ongoing research is to develop a practical method to produce tougher, more fatigue-resistant all-ceramic Dental restorations by modification with sputter-deposited thin-film surface coatings. Research conducted within the funded 6-year NIH project (once renewed) has focused on microstructural control of deposited films, assessing film effects on mechanical behavior of modified ceramic substrates, and characterization of film/environment interactions which affect film stress and substrate behavior. In the initial 3-year period yttria-stabilized zirconia (YSZ) was identified as the best thin-film ceramic coating material for the proposed application. It was demonstrated that YSZ thin-films produce no deleterious effect on bonding to a modified Dental ceramic surface, or on the esthetics of a translucent ceramic. In the second 3-year period, a unique interaction between deposited YSZ thin-films and environmental moisture was identified and characterized. TEM analyses of these films produced evidence of well defined and controllable tetragonal monoclinic phase transitions adjacent to internal defects. These can be manipulated to tailor film stress. Initial study of ductile/brittle polymer/YSZ laminate thin-films demonstrated promise for enhancement of fracture resistance of a brittle Dental substrate with control of the YSZ/water vapor interaction mechanism. Modeling of these structures indicates that specific thin-film structures can be created to provide optimal benefit in different environments. The proposed Specific Aims of this continued research are to: 1) Test the hypothesis that finite element analysis (FEA) of evolving YSZ thin-films, incorporating structural and stress state information, can predict the concentration/distribution of nano- and micro-dimensional defects, 2) Test the hypothesis that thin-film laminates with alternating ductile/brittle, low/high modulus (parylene/YSZ) layers will allow fine control of thin-film and film/substrate interfacial stress, allowing the direction (tensile, compressive, or zero) and magnitude of these stresses, and the interaction of the thin-film with the local environment to be controlled reproducibly, 3) Test the hypothesis that thin-film laminates with alternating ductile/brittle, low/high modulus layers will significantly enhance durability of traditional commercially available Dental ceramics, and 4) Demonstrate a viable technology for practical lab processing of varying permutations of YSZ and parylene/YSZ thin-films (development of a practical bench-top prototype deposition system). It is believed that this research will have a direct, positive impact on existing Dental ceramic technologies, enhancing the range of potential applications for low strength materials such as porcelain, and improving long term clinical efficacy. Development of non-metallic (e.g., amalgam-substitute) restorative materials is a high research priority due to biocompatibility issues and environmental concerns associated with metals waste and disposal. Ceramics offer the best combination of biocompatibility and environmental friendliness, but they have traditionally suffered from poor long-term clinical performance. The technology being investigated in this study has the potential to significantly improve the efficacy of existing Dental ceramics is a relatively simple manner.